Over years, microphones transforming sound wave to electrical signal are more and more used to communication industry (for example, telephone, mobile), multi-media computer system (VoIP), electronic toy (for example electronic game console, sound-controlled toy) and stereo equipment (for example DC, DV, MP3, MP4, hands-free audio frequency components) and other kind of products. The electret capacitance microphone (EMC) is widely applied in these industry. It usually includes: a metal shell surrounded by top surface and side wall with many hole-like sound channel on the top of the shell; a vibrating board inside the shell including a metal ring and a vibrating diaphragm on the ring-like head face; a back polar board; a plastic ring which is installed between the back polar board and metal ring, form a certain distance between the back polar board and vibrating diaphragm; a copper frame which is installed under the back polar board, connecting between the back polar board and the copper connect of circuit of technotron (JFET). In order to avoid the back polar board and copper frame being connected to the shell electricity, usually a plastic ring-like frame is installed outside of them for the insulation.
When the electret capacitance microphone is working, the sound wave enters into the shell through the hole-like channels to make vibration of the vibrating diaphragm. and the flat capacitance is formed by the vibrating diaphragm and the back polar board, thereby the vibration make the flat capacitance change too. Because, there is electret material on the vibrating diaphragm and back polar board, one of them is charged and the electret material on the one holds the electric charge too, thus there is stable quantity of electric charge in the capacitance. Therefore, the voltage between the two ends of the capacitance is changed by the distance changing between the positive and negative polar plates, so the formed acoustoelectric effect makes feeble electric signals, and then the electric signals go to a circuit board through a copper frame, and are transformed as required electrical signals by the circuit board.
When installation, put vibrating board inside the shell firstly, secondly put the plastic ring, then put the back polar board, copper frame and plastic frame in proper sequence, finally put the circuit board to seal the entrance and install the dust-proof clothing on the shell. It can be seen from the assembly, the total components are not less than 8 pieces, at least eight different procedures are needed, the cumulative error from each component will be big enough. Therefore, the manufacture accuracy is highly required, the assembling is difficult, that directly affect the product percent of pass, consistency of finished products, material cost and labor cost. Furthermore, the manufacture and assembling procedure is long, components are exposed in air for long time and many hand-operations, these disadvantages make components stick dust easily, these are serious affecting the sensitivity of product and the rate of product pass.